Offshore Waters Research Articles

The transition between coastal and offshore areas in the North Sea unraveled by suspended particle composition

Identifying the mechanisms that contribute to the variability of suspended particulate matter concentrations in coastal areas is important but difficult, especially due to the complexity of physical and biogeochemical interactions involved. Our study addresses this complexity and investigates changes in the horizontal spread and composition of particles, focusing on cross-coastal gradients in the southern North Sea and the English Channel. A semi-empirical model is applied on in situ data of SPM and its organic fraction to resolve the relationship between organic and inorganic suspended particles. The derived equations are applied onto remote sensing products of SPM concentration, which provide monthly synoptic maps of particulate organic matter concentrations (here, particulate organic nitrogen) at the surface together with their labile and less reactive fractions. Comparing these fractions of particulate organic matter reveals their characteristic features along the coastal-offshore gradient, with an area of increased settling rate for particles generally observed between 5 and 30 km from the coast. We identify this area as the transition zone between coastal and offshore waters with respect to particle dynamics. Presumably, in that area, the turbulence range and particle composition favor particle settling, while hydrodynamic processes tend to transport particles of the seabed back towards the coast. Bathymetry plays an important role in controlling the range of turbulent dissipation energy values in the water column, and we observe that the transition zone in the southern North Sea is generally confined to water depths below 20 m. Seasonal variations in suspended particle dynamics are linked to biological processes enhancing particle flocculation, which do not affect the location of the transition zone. We identify the criteria that allow a transition zone and discuss the cases where it is not observed in the domain. The impact of these particle dynamics on coastal carbon storage and export is discussed.

High-precision retrieval of offshore sea surface temperature: A machine learning framework based on MODIS and in-situ measurements

High-precision sea surface temperature (SST) data is essential for monitoring and management of offshore environment. SST retrievals from thermal infrared remote sensing have the advantages in time frequency and space coverage over measurements from ships and buoys. However, traditional SST retrieval models are not fully applicable for offshore waters where seawater conditions change a lot, due to simple functional forms and empirical fitting of model parameters. Machine learning (ML) is introduced because it doesn’t need to define specific model rules or unknown parameters, which is more intelligent to deal with complex retrieval problems in a data-driven way. But the applicability of ML has not been investigated in the North Yellow Sea of China, and the selection of driving features for model construction has not been fully discussed. Here, we designed a high-precision SST retrieval framework based on random forest (RF) with optimal feature combination using MODIS data and in-situ SST measurements during 2013–2020 in the northern part of the North Yellow Sea. The performances of different feature combinations were assessed based on model testing accuracies and the RF output feature importance. Compared with previous ML-based SST retrieval studies, we added two time-related features (i.e., day of the year and month) and one feature as initial temperature (i.e., SST retrieval from split-window algorithm), which reduced the testing error by around 15 % and 11 %, respectively. The retrieval results were validated with in-situ measurements, showing that the RF model achieved better accuracies (R2 = 0.987, SD = 0.842 °C, MAE = 0.675 °C, RMSE = 0.841 °C) than the improved split-window algorithm (named as ISW) and deep neural network. Compared with ISW, the spatial distribution of RF retrieval map exhibited similar variation across four seasons, mainly differed in the coastal areas or at the formation of temperature fronts. Note that the constructed RF model was still reliable when applied to the independent samples in 2021. This study contributes to improve the accuracy of offshore SST retrieval under different seawater conditions and provides references for SST monitoring.

Phytoplankton spring bloom in the NW Mediterranean Sea under climate change

The spring phytoplankton bloom is the main event influencing ecosystem richness in the pelagic realm of the Northwestern Mediterranean Sea (NW Med Sea). The Marine Strategy Framework Directive requires the achievement of a good ecological status for the pelagic habitat, and phytoplankton bloom phenology has been used as an indicator of the status of offshore waters. In this work we investigate interannual changes in the timing and magnitude of the phytoplankton bloom in the NW Med Sea, using phenological metrics. Daily maps of Chl-a concentration from 1998 to 2022 obtained by CMEMS were used to analyse bloom phenological metrics in 5 representative sites in the area. Chlorophyll-a data from 1998 to 2007 were used for determining the climatological behaviour, while 2008–2022 was identified as the study period. For this latter period, yearly spring bloom were identified and interannual variability and overall trends were analysed for each of the phenological metrics considered. Winter oceanographic and meteorological data were analysed to investigate possible correlations with the subsequent spring bloom. The frequency of anomalous years is increasing, both for bloom intensity and sea temperature. Bloom analysis revealed a negative trend only in some areas, but a steep decrease in the last 7 years was noticeable for all sites considered. Correlations of the Chl-a concentration during bloom with oceanographic variables revealed the importance of temperature, both marine and atmospheric, while Mixed Layer Depth played a lesser role. This work contributes to a better understanding of the dynamics of an area already under severe threat from human activities.

Biodegradation of Typical Plastics: From Microbial Diversity to Metabolic Mechanisms.

Plastic production has increased dramatically, leading to accumulated plastic waste in the ocean. Marine plastics can be broken down into microplastics (<5 mm) by sunlight, machinery, and pressure. The accumulation of microplastics in organisms and the release of plastic additives can adversely affect the health of marine organisms. Biodegradation is one way to address plastic pollution in an environmentally friendly manner. Marine microorganisms can be more adapted to fluctuating environmental conditions such as salinity, temperature, pH, and pressure compared with terrestrial microorganisms, providing new opportunities to address plastic pollution. Pseudomonadota (Proteobacteria), Bacteroidota (Bacteroidetes), Bacillota (Firmicutes), and Cyanobacteria were frequently found on plastic biofilms and may degrade plastics. Currently, diverse plastic-degrading bacteria are being isolated from marine environments such as offshore and deep oceanic waters, especially Pseudomonas spp. Bacillus spp. Alcanivoras spp. and Actinomycetes. Some marine fungi and algae have also been revealed as plastic degraders. In this review, we focused on the advances in plastic biodegradation by marine microorganisms and their enzymes (esterase, cutinase, laccase, etc.) involved in the process of biodegradation of polyethylene terephthalate (PET), polystyrene (PS), polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP) and highlighted the need to study plastic biodegradation in the deep sea.

Spatial and Temporal Variation of Satellite-Derived Chlorophyll-a in Bohai Sea over the Past 20 Years

The Chlorophyll-a (Chl-a) concentration in the surface layer of the Bohai Sea from 2003 to 2022 was obtained after processing the MODIS data with the improved shortwave infrared (SWIR) atmospheric correction algorithm and the Clack three-channel method. Its spatial and temporal variation were analyzed. The results show that it has obvious interannual spatial distribution characteristics, showing a trend of being high in nearshore waters and low in offshore waters, high in the estuarine bays and low in other sea areas. The interannual Chl-a variation shows an inverted U-shape. The year-by-year seasonal average spatial characteristics are basically consistent, with high in nearshore waters and low in other waters. The Chl-a in spring and summer was higher than that in autumn and winter. The temporal trend of the four seasons was similar to the interannual trend, showing an inverted U-shaped trend of first increasing, then stabilizing and then decreasing.

Offshore distribution of yelkouan shearwaters in the north-western Adriatic Sea

: The yelkouan shearwater Puffinus yelkouan is endemic to the Mediterranean and Black Seas, and classified as Vulnerable in the IUCN Red List. Information on the species’ distribution and habitat use in the eastern Mediterranean is scant, and only a few studies were based on direct visual observations in offshore waters. Here, we provide information on 1) the occurrence of yelkouan shearwaters within a 3000 km2 study area off the region of Veneto, Italy, in the northwestern Adriatic Sea, based on visual surveys conducted from small boats between April and October 2018–2022 (effort: 169 days, 23,836 km), and 2) the geographic, bathymetric and oceanographic variables likely to drive the species’ offshore distribution. Yelkouan shearwaters (238 sightings, 916 individuals) were observed in waters 9–33 m deep, between 2 and 24 km from the coast. Individual counts ranged between 1 and 100, with 95% of the encounters having less than 10 individuals. An Explainable Boosting Machine model – a machine learning technique based on generalized additive models – selected chlorophyll a as the most important variable to explain the species’ occurrence, followed by distance from the coast, and bottom depth. The model indicated a higher occurrence in waters with chlorophyll a less than ~2.3 mg/m3 , farther than ~15 km from the coast, and deeper than ~22 m. The effects of SST, salinity, and day of the year were less clear. This study provides insight into the offshore distribution of yelkouan shearwaters, within one of the Mediterranean areas most exposed to cumulative human threats

ResNet Deep Learning‐Based Inversion Method for Sea Surface Wind Field

This paper presents a method to invert the sea surface wind field from Sentinel‐1 synthetic aperture radar (SAR) interferometric wide swath (IW) band mode ground range detected (GRD) vertical polarization (VV) data based on the deep residual network (ResNet). Compared with the traditional algorithm (i.e., using geophysical model functions (GMFs)), the wind field inversion based on the ResNet deep learning method solves the problem of separate wind direction and wind speed inversion. The ResNet model is developed based on the results of 212 VV polarized IW images and cross calibrated multiplatform (CCMP) data collected in 2021 in the offshore waters of China. The root mean square error, standard deviation, and bias of the inverse wind direction of the ResNet model are 12.5°, 9.8°, and 7.4°, respectively, and the root mean square error, standard deviation, and bias of the inverse wind speed are 2.33, 1.495, and −1.375. The ResNet is better than the conventional local gradient and C‐band model models, further confirming the advantages shown by the deep learning algorithm in nonlinear fitting and its potential application in sea surface wind field inversion.

First record of the phyllosoma larva of the pygmy locust lobster Scyllarus pygmaeus (Crustacea, Decapoda) in the eastern Mediterranean sea

Abstract Taxonomic intricacies and high interspecific similarity have hampered the identification of scyllarid phyllosoma larvae to the species level. The pygmy locust lobster, Scyllarus pygmaeus, is distributed across the Mediterranean Sea and in the eastern Atlantic; however, its phyllosoma larvae were previously recorded only from the western Mediterranean. We employed DNA barcoding using the mitochondrial COI gene to identify S. pygmaeus phyllosoma collected from the offshore waters of the southeastern Mediterranean Sea and described its morphology. We further discuss the lack of genetic structure in S. pygmaeus with potential implications for species connectivity and conservation.

Environmental preferences and critical habitat for the velvet belly lanternshark (Etmopterus spinax) in Icelandic waters.

The velvet belly lanternshark (Etmopterus spinax) is a small, bioluminescent shark that is caught as bycatch in many deep-sea fisheries in the Atlantic Ocean. Using data from 10,597 seasonal research survey tows spanning 11 years, the distribution, relative abundance, life history, and environmental preferences of E. spinax in Icelandic waters was examined for the first time. E. spinax (n = 8774) were only captured in relatively deep offshore waters to the south and west of Iceland. Females grew to larger sizes than males and reached 50% sexual maturity at a total length of 50 cm. Females at a late stage of maturity and very small juveniles (<20 cm) were restricted to the central south Icelandic shelf, suggesting that this might be critical habitat for the reproduction of the species. Most of the sharks were captured at depths of 400-500 m, a relatively narrow depth range, and classified as a stenothermic warm-water species with habitat temperature restricted to about 6.3-8.0°C. Teleosts, crustaceans and cephalopods made up most of the diet. There was no indication of a decline in abundance over the time span of the survey. However, climate-induced warming of the deep ocean may shift the distribution of the species to more northerly waters within Iceland.

A remote sensing inversion method for offshore water depth considering geographical location characteristics

A remote sensing inversion method for offshore water depth considering geographical location characteristics

Broad scale community-level larval fish survey of southern Lake Erie

Abstract The early-life history stages of fish are sensitive to environmental change and therefore can indicate habitat quality as well as help predict recruitment of resident and transient fishes. In 2019, as part of the Lake Erie Cooperative Science and Monitoring Initiative, we conducted a lake-wide assessment of the ichthyoplankton community in U.S. nearshore waters and international offshore waters. The goal of this work was to characterize the larval fish community across the lake and assess species composition, phenology, and distribution of larvae. Ichthyoplankton were sampled weekly using bongo nets at ports beginning at the Detroit River and along the southern shore of Lake Erie to Dunkirk, NY, and less frequently in the Niagara River and offshore areas. Larval fish were present from March 26 through August 29, 2019. The first taxon to emerge was Lake Whitefish in all basins, followed by Walleye, Yellow Perch, and catostomids, depending on port. Mean total density peaked in mid-June due to high catches of Gizzard Shad, Morone spp., and Freshwater Drum in the western basin. Few fish were collected in the offshore sites. Taxa richness, diversity, and larval density were higher in the western basin and lower in the central and eastern basins, generally following the productivity gradient. This was the first study to provide a comprehensive community assessment of the ichthyoplankton community of Lake Erie and can provide a baseline to assess future change, especially in community composition or phenology, of larvae which are likely to respond to climate and habitat change.

A review of Eunicoidea (Annelida) from Falkland Islands waters including a new species of Hyalinoecia

Abstract Historic species records of the families Onuphidae and Eunicidae, from the Falkland Islands region, are reviewed and updated, new records added from intertidal and nearshore localities on and around the Falkland Islands, and a new species of Hyalinoecia described. Eight genera are reported from around the region including eight taxa of Onuphidae and two of Eunicidae, although most are only known from deep offshore waters. Kinbergonuphis dorsalis is re-described from type material, Kinbergonuphis sp. from the Falkland Islands is described and discrepancies between the two descriptions are examined. Hyalinoecia falklandica sp. nov. is described and the history of the genus and its misidentification in the region is discussed. The new species is distinguished from all other species in the genus through a combination of simple, unidentate falcigers on chaetigers 1 and 2, ventral cirri present to chaetigers 3 or 4, and branchiae present from chaetigers 26 or 27 to the end of the body. The historic record of Marphysa aenea from the Falkland Islands is also shown to be a misidentification and the actual, as-yet-undetermined species present is described. Problems surrounding a correct identification of Marphysa species, other species that do not quite fit current descriptions, and additional Eunicoidea taxa that might be expected to occur in the region are also discussed.

Integrated technology for layered sand control and layered water injection

In order to solve the problem of water injection string failure caused by pipe creep and sand production in layered water injection wells, an integrated technology of layered sand control and layered water injection has been developed. A suspended large-radiuslayered mechanical sand control pipe column has been designed, providing sufficient design and usage space for the layered water injection pipe column. Developing a new type of anti-creep sealed packer can effectively improve the anti-creep performance of the water injection string and extend the validity period of the string. This technology integrates and optimizes layered water injection and sand control technology, large channel backwashing technology, integrated testing and allocation technology, and anti-creep technology of the pipe string. While effectively solving sand production in offshore water injection wells, it extends the service life of the water injection pipe string and reduces operating costs. Since 2018, this technology has been implemented in over 200 wells in Chengdao Oilfield, with a maximum of 6 layers for prevention and injection, a maximum well inclination of 48.8°, and a construction success rate of over 90%. It has achieved very good development results and economic benefits.

Caribbean deepwater snappers: Application of the bomb radiocarbon age estimation validation in understanding aspects of ecology and life history.

Reef fishes have been utilized as food fish throughout the U.S. Caribbean and Gulf of Mexico waters for centuries, with increasing fishing effort in recent decades. As a result, many species have experienced declines in landings, including deepwater snappers such as queen snapper Etelis oculatus and blackfin snapper Lutjanus buccanella. However, little to no peer-reviewed published research exists on basic life history parameters for either species. Confirming the accuracy of an age estimation method for a fish species is essential for ensuring sustainable fisheries management. This is because in the assessment of fisheries species population age-based parameters, including longevity, age at sexual maturity, growth rate, mortality, age-specific reproductive output, and lifetime reproductive output, are important in understanding overall life history strategies of managed stocks. The past stock assessment on U.S. Caribbean queen snapper utilized an estimated longevity of 8 y, derived from length frequencies for fish from St. Lucia. Blackfin snapper has an estimated longevity of 27 y based on a relatively small study from offshore waters of the southeastern U.S. The focus of our investigation was to estimate maximum longevity of two data-poor species in the U.S. Caribbean. The accuracy of ageing methods was tested via bomb radiocarbon age estimation validation and effects of depth on Δ14C in otolith cores and eye lens core values were examined. Results from our work indicate a maximum validated age of 45 y for queen snapper, and 43 y for blackfin snapper. Our findings indicate queen snapper and blackfin snapper are long-lived (> 40 y). The resulting Δ14C comparison between eye lens cores and otolith cores has important implications for the study of age validation, specifically when deepwater species are involved.

Review of genus Halieutaea (Teleostei: Lophiiformes: Ogcocephalidae), with a new species from northern south China sea, named Halieutaea liui

In the offshore waters of Shantou, Guangdong Province, in the northern part of the South China Sea, a specimen belonging to the genus Halieutaea was collected at a depth of about 100 meters. It is similar to the known Halieutaea fitzsimonsi but also has some differences. Hence, this specimen is considered a neotype named Halieutaea liui sp. nov. The neotype can be distinguished from Halieutaea fitzsimonsi by the following external features: a prominent snout, a shorter peduncle, and unevenly distributed bony spines on the dorsal side of the disc. In addition, methods of distinguishing 13 known species of Halieutaea (including Halieutaea liui sp. nov.) by their appearance characteristics are cldwarified.

Temporal and spatial variation in the food web structure in artificial reef areas and adjacent habitats in Haizhou Bay

Artificial reef is regarded as an effective tool for restoring habitats and supporting the marine ecosystem. While the energy flow and material exchange in the food web of artificial reef ecosystem still remain vacant and should be further understood. In this study, stable isotopic characteristics (δ13C and δ15N) were used to identify the trophic niches and potential carbon sources of consumers (fish and invertebrates) in artificial reef areas and adjacent habitats in Haizhou Bay (the estuary area (EA), the aquaculture area (AA), the artificial reef area (AR), the natural area (NA) and the comprehensive effect area (CEA)) in spring and autumn. The results showed that the average δ13C for all consumers decreased from − 16.99 ± 2.07‰ to − 21.81 ± 1.66‰, and the average δ15N ranged from 11.37 ± 0.35‰ to 14.69 ± 0.64‰ in all seasons. A SIBER model revealed highly similar trophic niche among habitats in autumn, and lower overlap in spring. The SIMMR model showed that phytoplankton and sedimentary organic matter (SOM) were the major contributors to consumers, and particulate organic matter (POM) accounted for less contribution. In AA and NA phytoplankton and SOM generally contributed fairly equally to most fish, while single SOM sources were major contributors to nearly all the species in AR and CEA. Our findings reveal that ARs can serve as seascape mosaics to increase fish community diversity because of their high variation in the δ13C value and the trophic niches from EA to the NA. Preliminary multidisciplinary studies are needed for the mitigation of effects before any implementations deployed to the offshore waters that influence habitat connectivity, especially some habitat–specific migratory species.

Exposure of marine megafauna to cumulative anthropogenic threats in north-west Australia

As the use of coastal and offshore environments expands, there is a need to better understand the exposure of marine megafauna to anthropogenic activities that potentially threaten their populations. Individual satellite telemetry studies are often hampered by small sample sizes, providing limited information on spatiotemporal distributions of migratory animals and their relationships to anthropogenic threats. We addressed this issue by synthesising satellite tracking data from 484 individuals of three taxonomic groups and six species; three marine turtle, two whale and one shark. The spatial overlap between taxa distributions and multiple anthropogenic activities was assessed as a proxy for the cumulative exposure of these taxa to anthropogenic threats (coastal modification, vessel strike, underwater noise, oil spill, bycatch, entanglement, and artificial light) across an area totalling 2,205,740 km2 off north-western Australia. Core exposure areas (top 50% of the distribution) encompassed ecologically important sites for all taxa, such as the Ningaloo and Pilbara regions, migratory routes for whales and sharks in offshore waters beyond Ningaloo Reef, and marine turtle nesting beaches at Barrow Island and Cape Lambert. Although areas of high exposure represented &amp;lt;14% of taxa distributions, we showed that no taxa occurred in the absence of threats and that even areas with existing spatial protections are experiencing high levels of exposure. Importantly, we developed a robust approach for documenting the potential exposure of marine species to a range of human activities at appropriate spatial scales to inform conservation management.

The Predictability of the 30 October 2020 İzmir-Samos Tsunami Hydrodynamics and Enhancement of Its Early Warning Time by LSTM Deep Learning Network

Although tsunamis occur less frequently compared to some other natural disasters, they can be extremely devastating in the nearshore environment if they occur. An earthquake of magnitude 6.9 Mw occurred on 30 October 2020 at 12:51 p.m. UTC (2:51 p.m. GMT+03:00) and its epicenter was approximately 23 km south of İzmir province of Turkey, off the Greek island of Samos. The tsunami event triggered by this earthquake is known as the 30 October 2020 İzmir-Samos (Aegean) tsunami, and in this paper, we study the hydrodynamics of this tsunami using some of these artificial intelligence (AI) techniques applied to observational data. More specifically, we use the tsunami time series acquired from the UNESCO data portal at different stations of Bodrum, Syros, Kos, and Kos Marina. Then, we investigate the usage and shortcomings of the Long Short Term Memory (LSTM) DL technique for the prediction of the tsunami time series and its Fourier spectra. More specifically we study the predictability of the offshore water surface elevation dynamics, their spectral frequency and amplitude features, possible prediction success and enhancement of the accurate early prediction time scales. The uses and applicability of our findings and possible research directions are also discussed.

The effect of alongshore wind stress on a buoyancy current’s stability

Buoyancy fronts reach from the surface to the bottom over continental shelves, separating light inshore water from denser offshore water, and are known to be responsive to Ekman transport (and associated return flow at depth) driven by alongshore winds. The consequent changes in frontal structure are clearly related to changes in the gravitational Available Potential Energy (APE), so it is reasonable to expect that these winds will affect the eddy field that results from baroclinic instabilities. Idealized numerical experiments and scaling analyses are brought to bear on this problem. It is found that several days of wind-driven downwelling (which creates more nearly vertical isopycnals) generally leads to an enhancement in the time maximum of volume-averaged Eddy Kinetic Energy (EKE). Upwelling-favorable winds (which tend to flatten isopycnals) usually lead to a decrease in APE, hence in eddy energy. The exception to this rule occurs when the winds are strong enough that an upwelling front forms inshore of the buoyant water, in which case APE and EKE may increase.

LEADING MODES AND FEATURE ZONES OF SEA ICE CONCENTRATION IN NORTH PACIFIC DURING SPRING SEASONS OF 2000–2020

Under the influence of the Arctic amplification, sea ice variability in North Pacific is becoming a key indicator of global climate changes. Due to the widespread and complex impacts of North Pacific sea ice variations, the understanding of its dynamic changes, especially its spatial and temporal evolution patterns, has great significance. In this study, we used the rotated empirical orthogonal decomposition to divide the whole North Pacific into six feature zones on the evolution sea ice concentration under the recent global warming and highlighted the complexity and diversity of sea ice variations in the offshore waters.